Skull: Anatomy

Viscerocranium

The viscerocranium is responsible for maintaining the structure for the muscles of the face Muscles of the Face The facial muscles (also called mimetic muscles) control facial expression and are supplied by the facial nerve. Most of them originate from the skull and attach to the skin around the facial openings, which serve as a method to group or classify them. Facial Muscles: Anatomy. The muscles are arranged in a complex anatomical pattern to allow for a variety of facial functions such as mastication Mastication The act and process of chewing and grinding food in the mouth. Jaw and Temporomandibular Joint: Anatomy, smiling, frowning, eye movement, and patency of the nasal passage.

Neurocranium

The neurocranium is the complex of bones encasing the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification. The calvarium is the upper portion of the neurocranium, and consists of the unpaired frontal bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types, unpaired occipital bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types, bilateral parietal bones, and bilateral temporal bones. The bones are initially separated (the fontanelles Fontanelles Physical Examination of the Newborn at birth) and fuse over childhood. The bones are then connected by specific sutures: coronal Coronal Computed Tomography (CT), squamous, lambdoid, and sagittal Sagittal Computed Tomography (CT).

Bones of the neurocranium:

• Frontal bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types
• Occipital bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types
• Parietal bones (2)
• Temporal bones (2)
• Ethmoid bone Ethmoid bone A light and spongy (pneumatized) bone that lies between the orbital part of frontal bone and the anterior of sphenoid bone. Ethmoid bone separates the orbit from the ethmoid sinus. It consists of a horizontal plate, a perpendicular plate, and two lateral labyrinths. Orbit and Extraocular Muscles: Anatomy
• Sphenoid bone Sphenoid bone An irregular unpaired bone situated at the skull base and wedged between the frontal, temporal, and occipital bones (frontal bone; temporal bone; occipital bone). Sphenoid bone consists of a median body and three pairs of processes resembling a bat with spread wings. The body is hollowed out in its inferior to form two large cavities (sphenoid sinus). Orbit and Extraocular Muscles: Anatomy

Main sutures are immobile joints between adjacent bones of the skull:

• Coronal Coronal Computed Tomography (CT): between the frontal and parietal bones
• Sagittal Sagittal Computed Tomography (CT): between the parietal bones, along the midline
• Lambdoid: between the parietal and occipital bones 
• Squamous: between the parietal and temporal bones

Major fontanelles Fontanelles Physical Examination of the Newborn are areas of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology within the gaps/between the bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types plates, which are open during infancy:

• Posterior, occipital, or lambdoid
• Anterior, bregmatic, or frontal
• Sphenoidal or anterolateral
• Mastoid or posterolateral

Base of the Skull

The skull base is a highly complex region of the skull with many important anatomical landmarks and foramen for cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. The 12 Cranial Nerves: Overview and Functions and vasculature to travel in and out of the skull. In-depth knowledge of the location of the foramen and the structures traversing the foramen are critically important.

External Fossae

Clinical Relevance

• Le Fort fractures Le Fort fractures Le Fort fractures are a group midface fracture patterns classified into 3 types: Le Fort I, II, and III. Le Fort fractures represent 10%-20% of all facial fractures and can be caused by any significant blunt trauma to the face, most commonly from motor vehicle accidents. Le Fort Fractures: transverse fractures of the midface. Three types of Le Fort fractures Le Fort fractures Le Fort fractures are a group midface fracture patterns classified into 3 types: Le Fort I, II, and III. Le Fort fractures represent 10%-20% of all facial fractures and can be caused by any significant blunt trauma to the face, most commonly from motor vehicle accidents. Le Fort Fractures exist and involve the separation of all or a portion of the midface from the skull base. The fractures are repaired surgically by adding stabilizing plates.
• Skull fractures: an interruption in the continuation of the bones comprising the calvarium. The fractures usually occur due to blunt force trauma and are often associated with a traumatic brain injury Traumatic brain injury A form of acquired brain injury which occurs when a sudden trauma causes damage to the brain. Le Fort Fractures. Fractures of the pterion may rupture the middle meningeal artery Middle Meningeal Artery Epidural Hemorrhage. Fractures of the petrous portion of the temporal bone Temporal bone Either of a pair of compound bones forming the lateral (left and right) surfaces and base of the skull which contains the organs of hearing. It is a large bone formed by the fusion of parts: the squamous (the flattened anterior-superior part), the tympanic (the curved anterior-inferior part), the mastoid (the irregular posterior portion), and the petrous (the part at the base of the skull). Jaw and Temporomandibular Joint: Anatomy may cause blood or cerebrospinal fluid Cerebrospinal Fluid A watery fluid that is continuously produced in the choroid plexus and circulates around the surface of the brain; spinal cord; and in the cerebral ventricles. Ventricular System: Anatomy to escape from the ear, which may result in hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss. 
• Orbital fractures Orbital fractures An orbital fracture is a break in the continuity of one or multiple bones of the eye socket, caused by direct or indirect trauma to the orbit. Patients frequently present with lacerations around the eye, orbital pain, edema, ecchymosis, diplopia on upward gaze, numbness around the eye, and signs of muscle entrapment. Orbital Fractures: fractures to the eye sockets. Orbital fractures Orbital fractures An orbital fracture is a break in the continuity of one or multiple bones of the eye socket, caused by direct or indirect trauma to the orbit. Patients frequently present with lacerations around the eye, orbital pain, edema, ecchymosis, diplopia on upward gaze, numbness around the eye, and signs of muscle entrapment. Orbital Fractures are classified as orbital rim Orbital Rim Orbital Fractures fractures, direct orbital floor Orbital Floor Orbital Fractures fractures, and blowout fractures. Individuals present with bruising around the eyes accompanied by blurry, decreased, or double vision Vision Ophthalmic Exam.
• Craniosynostosis Craniosynostosis Craniosynostosis is the premature fusion of 1 or more cranial sutures during the 1st year of life. Craniosynostosis is classified as simple or complex, and can be caused by environmental factors or genetic syndromes. Craniosynostosis: the premature Premature Childbirth before 37 weeks of pregnancy (259 days from the first day of the mother’s last menstrual period, or 245 days after fertilization). Necrotizing Enterocolitis fusion of 1 or more cranial sutures. Craniosynostosis Craniosynostosis Craniosynostosis is the premature fusion of 1 or more cranial sutures during the 1st year of life. Craniosynostosis is classified as simple or complex, and can be caused by environmental factors or genetic syndromes. Craniosynostosis can be classified as simple or complex and typically results in an abnormally shaped head. Craniosynostosis Craniosynostosis Craniosynostosis is the premature fusion of 1 or more cranial sutures during the 1st year of life. Craniosynostosis is classified as simple or complex, and can be caused by environmental factors or genetic syndromes. Craniosynostosis occurs in approximately 4 per 10,000 children and can be improved with surgical intervention.
• Acrania: a rare congenital disorder characterized by the partial or complete absence of the bones of the skull. The condition is commonly associated with anencephaly Anencephaly A malformation of the nervous system caused by failure of the anterior neuropore to close. Infants are born with intact spinal cords, cerebellums, and brainstems, but lack formation of neural structures above this level. The skull is only partially formed but the eyes are usually normal. This condition may be associated with folate deficiency. Affected infants are only capable of primitive (brain stem) reflexes and usually do not survive for more than two weeks. Neural Tube Defects. 
• Cranium bifidum: a neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation defect characterized by the improper closure of the fetal skull during development. Cranium bifidum is usually associated with encephalocele Encephalocele Brain tissue herniation through a congenital or acquired defect in the skull. The majority of congenital encephaloceles occur in the occipital or frontal regions. Clinical features include a protuberant mass that may be pulsatile. The quantity and location of protruding neural tissue determines the type and degree of neurologic deficit. Visual defects, psychomotor developmental delay, and persistent motor deficits frequently occur. Neural Tube Defects or the protrusion of cerebral matter covered by meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges: Anatomy through the bony defect. Presentation typically includes a groove down the midline of the skull between the forehead Forehead The part of the face above the eyes. Melasma, nose Nose The nose is the human body’s primary organ of smell and functions as part of the upper respiratory system. The nose may be best known for inhaling oxygen and exhaling carbon dioxide, but it also contributes to other important functions, such as tasting. The anatomy of the nose can be divided into the external nose and the nasal cavity. Nose Anatomy (External & Internal), or occipital region.